Datasheet
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5 Power Supplies
6 Using the EVM
6.1 As a Reference Board
Power Supplies
The EVM accepts four power supplies.
• A dual ± V
S
dc supply for the dual supply operational-amplifiers. Recommended ± 5 VDC.
• A single 2.7 to 5-V dc supply for U3, the ADC supply reference (2.5-V, REF3225).
• A single 1.8 to 3.3-V dc supply for digital section of the board (output buffers U6).
There are two ways to provide these voltages.
1. Wire in voltages at test points on the EVM. See Table 4 .
Table 4. Power Supply Test Points
Test Point Signal Description
TP1 +VA Apply +5 VDC. Positive supply for amplifier.
TP2 –VA Apply -5 VDC. Negative supply for amplifier.
TP3 +VDD Apply up to 3.6 VDC. See the ADC data sheet for full range.
TP15 +VCC via W3 and W4 Apply up to 3.6 VDC max and move the jumper at W3 to cover pins 2-3.
2. Use the power connector J2, and derive the voltages elsewhere. The pin out for this connector is
shown in Table 5 . If using this connector, then set W2 jumper to connect +3.3VD from connector to
+VDD. A short between pins 1-2 to select +3.3VD as the source for the digital I/O buffer voltage supply
(+IOVDD) is the factory shipped condition.
Table 5. Power Connector Pin Out
Signal J1 Pin Signal
+VA (5 V) 1 2 –VA (–5 V)
+5VA 3 4 N/C
DGND 5 6 AGND
N/C 7 8 N/C
+3.3VD 9 10 +5VD
The voltage applied to the VCC pin of the ADC is controlled by W4. Pin 1 of W4 is cut to prevent the
+5VCC from being applied to the ADC. By default, pins 2 and 3 are shorted and the reference voltage
selected by W3 is powering the ADC. To monitor device current draw, the shunt jumper can be removed
and replaced with a current meter. See Table 2 or the schematic drawings at the end of this user’s guide
to determine how power is supplied to the various ICs on the board.
The ADS7866/ADS7867/ADS7868EVM serves three functions:
1. As a reference design
2. As a prototype board and
3. As software test platform
As a reference design, the ADS7866EVM/ADS7867EVM/ADS7868EVM contains the essential circuitry to
showcase the A/D converter. This essential circuitry includes the input amplifier, reference circuit, and
buffers. The analog input circuit is optimized for 100-kHz input signal; therefore, users may need to adjust
the resistor and capacitor values to accommodate higher frequencies and different test systems. In
ac-type applications where signal distortion is concern, care should be taken to insure polypropylene or
C0G type capacitors are used in the signal path.
The design and layout of this EVM, in conjunction with the ADC data sheet, can be used as the guide
when incorporating this ADC into the user system board.
SLAU181 – July 2006 ADS7866EVM/ADS7867EVM/ADS7868EVM 5
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